1. Field of the Disclosure
The disclosure relates to impact-modified polycarbonate compositions and moulding compositions comprising an emulsion graft polymer precipitated under basic conditions and acidic phosphorus compounds, which are distinguished compared with the prior art by an improved combination of stability to hydrolysis and heat stability, and which are suitable for production of injection-moulded components which have a good toughness at low temperatures and—even with critical processing conditions (high processing temperatures)—still have a good resistance to stress cracking under the influence of chemicals.
2. Description of Related Art
Emulsion graft polymers which are employed as impact modifiers in polycarbonate compositions of the prior art are in general worked up under acidic conditions, i.e. dispersions of such graft polymers in distilled water have an acidic pH. This is necessary in order to ensure an adequate heat stability of the polycarbonate compositions, since basic components as is known tend to thermally degrade the polycarbonate under processing conditions. Such polycarbonate compositions comprising emulsion graft polymers which have been precipitated under acidic conditions are often additionally stabilized during compounding by addition of acidic heat stabilizers. Such compositions as a rule indeed have a good heat stability, but in general they have a lack of stability towards hydrolytic cleavage of the polycarbonate under the influence of humid heat ageing.
EP-A 900 827 discloses impact-modified polycarbonate compositions with improved heat stability comprising emulsion polymers which are substantially free from any basic components which degrade the polycarbonate. According to this application, such polycarbonate compositions which are impact-modified with emulsion polymers which contain basic impurities due to the preparation have a lack of heat stability.
EP-A 576 950 and WO-A 2007/065579 describe compositions which contain basic impurities and comprise polycarbonate and acrylonitrile/butadiene/styrene (ABS) polymers, and are stabilized with multifunctional organic carboxylic acids. Such compositions have a good heat stability with respect to the integrity of the molecular weight of the polycarbonate component at high processing temperatures, but in injection moulding tend towards the formation of surface defects (streaks) on the mouldings produced from them.